1. Field of the Invention
The present invention relates to a radial tire for passenger vehicles, and in particular, to a bead structure which improves the stability and controllability of a radial tire including a pair of bead cores provided at bead portions, a carcass ply extending in a toroidal shape from one bead portion to the other bead portion and wound about the bead cores and anchored to the bead portions and formed from one radial cord layer, a belt and a tread disposed at a crown portion radial direction outer side of the carcass ply, bead fillers respectively starting from a radial direction outer side of a bead core and tapering toward the outer side, and bead reinforcing layers respectively disposed at a bead portion.
2. Description of the Related Art
A radial tire for passenger vehicles having a carcass ply formed from one radial cord layer is advantageous in that it has a simple structure and is lightweight. However, the rigidity of the bead portions is insufficient, which is disadvantageous with respect to stability and controllability. Therefore, attempts have been made to reinforce the bead portions by various methods such as increasing the volume of the bead fillers and using a rubber having a relatively high hardness (i.e., a rubber having a high JIS A hardness value). However, there are limits as to the extent to which improvements in the bead filler can improve stability and controllability.
In addition, recently further improvements in stability and controllability have been required from the demand for better vehicle performance and for safer driving, and in order to meet the requirements, reinforcing the bead portions, apart from the bead fillers themselves, with organic fibers (e.g., aromatic polyamide fibers, commercial name "KEVLAR" produced by Du pont, referred to herein as aramid), or inorganic fibers such as steel cords or the like have become standard for high performance tires in particular.
Nevertheless, in the case in which the beads are reinforced with steel cord layers, although rigidity is increased, the weight increases, the comfort of the ride deteriorates, and separation occurs at the steel cord ends which is a cause for trouble. In the case in which the aramids having a high cord modulus of elasticity are used as a reinforcing material, the structure is lightweight and has great effects, but is extremely disadvantageous from the point of view of cost.